1. Field of the Invention
The present invention relates generally to an anchoring assembly for a downhole tool. The anchoring assembly includes an improved cone and slip assembly system to set a downhole tool in a wellbore. The improved cone and integral slip assembly are adapted to interact break the slip assembly into slip segments at predetermined locations as the integral slip assembly traverses the cone. The improved cone and integral slip assembly are adapted to facilitate the centering of a packing element when setting the downhole tool in the wellbore.
2. Description of the Related Art
The drilling and servicing of gas and oil wells often requires the isolation of certain zones within the well. Typically, the isolation of a zone is accomplished by the insertion of a downhole tool, such as a bridge plug, fracturing plug, or cement retainer, into the wellbore. The purpose of the tool is simply to isolate a portion of the well from another portion or the rest of the well. For instance, perforations in the well in one portion may need to be isolated from perforations in another portion of the well, or there may be a need to isolate the bottom of the well from the wellhead. Further, a permanent plug may be used to permanently close off and abandon the well.
A downhole tool, such as typical wellbore plug, generally is comprised of an anchoring assembly arranged about a mandrel that is run into the wellbore. The anchoring assembly typically includes a plurality of slips and a cone, as well as an elastomeric packing element. The slips may be arranged in a slip ring, or the slips may be initially formed in a ring, the slips being designed to break apart upon the application of an axial load. Regardless, the slips include a tapered surface that is adapted to mate with a tapered surface of the cone. As an axial force is applied to the downhole tool, the slips ride up on the tapered surface of the cone, and are thus driven outwardly, away from the mandrel, and into the wellbore to set the tool.
Specifically, the downward force applied to the anchoring assembly causes the upper slips to move up the upper cone. As the upper slip traverses the upper cone, the tapered shape of the upper cone moves the upper slip outward and the upper slip engages the casing wall, thus locking the anchoring assembly in place within the well. Once the anchoring assembly is locked within the well, the upward force moves the lower portion of the assembly (i.e., lower cap, lower cone, and lower slip) upward toward the upper portion of the assembly. Because the upper portion is anchored against the wall, the movement of the lower portion axially compresses the packing element.
Further application of axial force compresses the elastomeric packing element, driving the packing element outwardly to contact and seal against the wellbore. The axial compression of the packing element causes the packing element to expand radially against the well casing creating a sealing barrier that isolates a portion of the well. Once the packing element has been compressed and radially expanded, the upward force causes the lower slip to traverse the lower cone.
The tapered shape of the lower cone moves the lower slip outward until it engages the well casing, thus locking the lower portion of the anchoring assembly in place within the well. The locking of the lower portion of the anchoring assembly ensures that the packing element remains radially expanded against the well casing while the downhole tool is set.
When setting the packing element, it is important that the packing element be centered within the wellbore so that a uniform, circular extrusion gap exists around the packing element. Packing elements are design to expand evenly against the well casing. If not centered within the well, it will be more difficult for the packing element to completely bridge the gap to create a seal and isolate a portion of the well. In order to bridge an uneven gap, an excessive downward force may be needed to set the packer. This increased force as well as the uneven expansion of the packing element against the wellbore may cause the premature failure of the packing element.
As described above, present anchoring assemblies may include a solid slip ring, placed about the mandrel. Alternatively, solid slip rings are known which are adapted to break into individual slips during the setting operation. Each of these slip ring helps to ensure the central alignment of the assembly and the packing element within the well.
However, it is not uncommon for these prior art slip rings to break in the single weakest spot along the ring. This spot may be the weakest due to a variance in material thickness or a pre-existing defect.
A solid slip ring having a single axial break is herein after referred to as a “c-ring.” While the c-ring may still properly anchor the assembly after traversing the cone, the anchoring assembly may shift on the mandrel to the same orientation as the break of the c-ring. Thus, the c-ring does not properly center the packing element within the well leading to the possibility that the packing element will prematurely fail, as described above.
In light of the foregoing, it would be desirable to provide a slip assembly that does not break at an area of weakness into a c-ring, but rather accurately breaks into a plurality of designated slip segments. Further, it would be desirable to provide a solid slip ring that as it traverses the cone breaks into designated segments that ensure that the packing element is centered within the wellbore.
Further, removal of the components of downhole tools can be problematic. For example, once the plug described above has performed its function and it is desired to remove the plug, a drill or mill is run downhole to remove the plug. In some instances, components of the downhole tool, which contact the drill or mill during the removal process, begin to rotate with the drill or mill. The drill or mill cannot effectively grind away this component which is rotating with the mill or drill, thus hampering the removal. It would be desirable to provide components of the downhole tool with an anti-rotational mechanism to prevent rotation of the components of the downhole tool during removal. It would further be desirable to provide a solid slip ring that engages a structure on the mandrel adapted to prevent rotation of the anchoring assembly with respect to the mandrel.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.